![Artist’s impression of Corot-7b](https://upload.wikimedia.org/wikipedia/commons/9/93/Artist%E2%80%99s_impression_of_Corot-7b.jpg)
A lava planet is a type of
terrestrial planet
A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, Ve ...
, with a surface mostly or entirely covered by molten
lava
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...
. Situations where such planets could exist include a young terrestrial planet just after its formation, a planet that has recently suffered a large collision event, or a planet orbiting very close to its
star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
, causing intense irradiation and
tidal force
The tidal force is a gravitational effect that stretches a body along the line towards the center of mass of another body due to a gradient (difference in strength) in gravitational field from the other body; it is responsible for diverse phenomen ...
s.
Factors and characteristics
Lava planets would probably orbit extremely close to their parent star. In planets with eccentric orbits, the gravity from the nearby star would distort the planet periodically, with the resulting friction producing
internal heat
{{Unreferenced, date=February 2012
Internal heat is the heat source from the interior of celestial objects, such as stars, brown dwarfs, planets, moons, dwarf planets, and (in the early history of the Solar System) even asteroids such as Vesta, r ...
. This
tidal heating
Tidal heating (also known as tidal working or tidal flexing) occurs through the tidal friction processes: orbital and rotational energy is dissipated as heat in either (or both) the surface ocean or interior of a planet or satellite. When an objec ...
could melt rocks into
magma
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...
, which would then erupt through
volcano
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plates are ...
es. This would be similar to the Solar System moon
Io, orbiting close to its parent
Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
. Io is the most geologically active world in the Solar System, with hundreds of volcanic centres and extensive lava flows. Lava worlds orbiting extremely closely to the parent star may possibly have even more volcanic activity than Io, leading some astronomers to use the term ''super-Io''. These "super-Io" exoplanets may resemble Io with extensive sulfur concentrated on their surfaces that is associated with the continuous active volcanism.
However, tidal heating is not the only factor shaping a lava planet. In addition to tidal heating from orbiting close to their parent star, the intense stellar irradiation could melt the surface crust directly into lava. The entire star-facing surface of a
tidally locked
Tidal locking between a pair of co-orbiting astronomical body, astronomical bodies occurs when one of the objects reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit. In the case where ...
planet could be left covered in a lava ocean while the nightside may have
lava lake
Lava lakes are large volumes of molten lava, usually basaltic, contained in a volcanic vent, crater, or broad depression. The term is used to describe both lava lakes that are wholly or partly molten and those that are solidified (someti ...
s, or even lava rain caused by the condensation of vaporized rock from the dayside. The mass of the planet would also be a factor. The appearance of
plate tectonics
Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...
on terrestrial planets is related to planetary mass, with more massive planets than Earth expected to exhibit plate tectonics and thus more intense volcanic activity. Also, a
Mega Earth may retain so much internal heat from its formation that a solid crust cannot form.
Protoplanet
A protoplanet is a large planetary embryo that originated within a protoplanetary disc and has undergone internal melting to produce a differentiated interior. Protoplanets are thought to form out of kilometer-sized planetesimals that gravitation ...
s tend to have intense volcanic activity resulting from large amounts of
internal heating
{{Unreferenced, date=February 2012
Internal heat is the heat source from the interior of celestial objects, such as stars, brown dwarfs, planets, moons, dwarf planets, and (in the early history of the Solar System) even asteroids such as Vesta, re ...
just after formation, even relatively small planets that orbit far from their parent stars. Lava planets can also result from giant impacts; Earth was briefly a lava planet after being impacted by
a Mars-sized body which
formed the Moon.
A 2020
preprint
In academic publishing, a preprint is a version of a scholarly or scientific paper that precedes formal peer review and publication in a peer-reviewed scholarly or scientific journal. The preprint may be available, often as a non-typeset versio ...
study finds that lava planets have low
geometric albedo
In astronomy, the geometric albedo of a celestial body is the ratio of its actual brightness as seen from the light source (i.e. at zero phase angle) to that of an ''idealized'' flat, fully reflecting, diffusively scattering ( Lambertian) disk w ...
s of around 0.1 and that molten lava on the surface can cool and harden to form
quenched glass.
Candidates
There are no known lava worlds in the
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
and the existence of extrasolar lava planets remains unknown. Several known exoplanets are likely lava worlds, given their small enough masses, sizes, and orbits. Likely lava exoplanets include
COROT-7b
CoRoT-7b (previously named CoRoT-Exo-7b) is an exoplanet orbiting the star CoRoT-7 in the constellation of Monoceros (constellation), Monoceros, from Earth. It was first detected Methods of detecting extrasolar planets#Transit photometry, photome ...
,
Kepler-10b
Kepler-10b is the first confirmed terrestrial planet to have been discovered outside the Solar System by the Kepler Space Telescope. Discovered after several months of data collection during the course of the NASA-directed Kepler Mission, which ...
, and
Kepler-78b
Kepler-78b (formerly known as KIC 8435766 b) is an exoplanet orbiting around the star Kepler-78. At the time of its discovery, it was the exoplanet most similar to Earth in terms of mass, radius, and mean density.
Discovery
Kepler-78b is the only ...
.
See also
*
Chthonian planet
Chthonian planets (, sometimes 'cthonian') are a hypothetical class of celestial objects resulting from the stripping away of a gas giant's hydrogen and helium atmosphere and outer layers, which is called hydrodynamic escape. Such atmospheric ...
*
List of planet types
The following is a list of planet types by their mass, orbit, physical and chemical composition, or by another classification.
The IAU defines that a ''planet'' in the Solar System must orbit around the Sun, has enough mass to assume hydrostat ...
*
Magma ocean Magma oceans exist during periods of Earth's or any planet's Accretion (astrophysics), accretion when the planet is completely or partly molten.
In the early Solar System, magma oceans were formed by the melting of Planetesimal, planetesimals and ...
*
Mustafar
Mustafar () is a fictional volcanic and lava planet in the ''Star Wars'' franchise. Introduced in the final prequel film, ''Revenge of the Sith'' (2005), it also appeared in the films ''Rogue One'' (2016) and ''Episode IX – The Rise of Skywal ...
(fictional planet)
*
Lava planets in science fiction
References
Further reading
Lava Worlds: From Early Earth to Exoplanets Keng-Hsien Chao, Rebecca deGraffenried, Mackenzie Lach, William Nelson, Kelly Truax, Eric Gaidos, 14 Dec 2020
{{Portal bar, Astronomy, Space
*
Types of planet